Train carried cab signal apparatus



Feb. 22, 1949.y

l.. R. ALLlsoN TRAIN'CARRIED CAB SIGNAL APPARATUS Filed April 9, 1947 .wm Sw sww EN llillllll THQ@ wmmwwwwrm I N V EN TOR. [es Allison.

`fil/f ,4r/mmv Patented Feb. 22, 1949 U TED STAT S ATENT OFFICE TRAIN CARRIED CAB SIGNAL APPARATUS Application April 9, 1947, Serial No. 740,311

4 Claims.

My invention relates to train carried cab signal apparatus, and more particularly to cab signal apparatus responsive to coded track circuit energy.

The coded current for influencing cab signal apparatus of the type here contemplated is generally supplied across the track rails at the exit end of a track section so that current flows in one rail through the train shunt and back in the other rail when a train occupies the section. Two inductors are mounted on the train ahead of the leading pair of wheels with one inductor over each rail to inductively pick up an electromotive force due to the rail current. The general practice is to use alternating current of the order of 100 cycles per second and to code the current by periodically interrupting it at the rates of 180, 120 and 75 times per minute according to clear, approach-medium and approachy traliic conditions in advance of the track section. In some systems only two codes of the rates of 180 and 75 interruptions per minute are used .to reflect clear and approach traffic conditions, and it is apparent that additional codes can be used to reflect additional traffic conditions if desired.

The electromotive forces picked up by the inductors have the frequency and code rate of the rail current, and the two inductors are connected for their two electromotive forces to add their eiiects. amplied and used tc operate a code following relay which governs decoding units that are 'selectively responsive to the code rate at whichv the relay is operated. The decoding units govern in turn cab signals and other warning devices through a group of decoding relays, there being an individual decoding relay for each decoding unit.

Acknowledging means is generally provided with cab signal apparatus oi this type wherewith the train operator or engineman is required to acknowledge a change in the cab signal indication when the change is to a more restrictive indication.

The requisites of cab signal apparatus are very exacting because the safety of the train is involved. For example, the requisites require the apparatus to have a sensitivity that assures satisfactory train shunt detection and broken rail protection@ Als-o, a substantially uniform response over a relatively wide range in the magnitude of the rail current as caused by different local conditions and the shunting out of the rail impedance when the train moves toward the exit end of the section is necessary. The amplifier The resulting 'electromotive force is must be immune to extraneous energy picked up by the inductors due to the rails carrying propulsion current and stray currents from power systems. Also, operation of the apparatus must be satisfactory when the train carried Source from which energy is derived for energizing the apparatus varies widely in its voltage. Code distortion must be minimized. False operation due to broken or misplaced circuit elements must be avoided. Ample manufacturing tolerance must be permitted. The apparatus must withstand severe vibrations and shocks due to train movements. Again, the apparatus must be such that inspection and testing can readily and quickly be made before trains leave the terminal.

In view of the foregoing and additional requisites, a main object of my invention is the provision of improved cab signal apparatus having a high order of reliability of operation and having a simple construction.

Another feature of my invention is the provision of cab signal apparatus of the type here involved incorporating improved decoding means to increase the margin against the possibility of false operation due to an intermittent circuit fault.

Again, a feature of my invention is the provision of improved cab signal apparatus having identical decoding and acknowledging relays for complete interchangeability.

Another feature of my invention is the provision of cab signal apparatus incorporating a novel arrangement of acknowledging circuitsf wherewith the time between the reception of a more restrictive code and the initiating of a warning signal is varied inversely starting from the clear code.

A further feature of my invention is the provision of cab signal apparatus incorporating an improved manner of housing to facilitate inspection and maintenance.

Other features, objects and advantages of my invention will appear as the specication progresses.

The foregoing objects, features and advantages of my invention I attain by provision of a single stage low voltage amplier unit, decoding units, one for each code, and each unit tuned to resonance at a frequency corresponding to the respective code, decoding relays and acknowledging relays identical in construction, a test panel and a circuit network, the vital circuits of which are of a double break type. This apparatus is grouped in an assembly that is arranged to afford a high order of protection against vibration, shock For a fuller understanding of my invention,

reference may be had to the accompanying drawing, which is a diagrammatic View showing one form of apparatus embodying my invention when Y used with a four indication cab signal system for railways.

It is to be understood that the invention is not limited to a four indication cab signal system,

and this application serves to illustrate the many places the apparatus is useful.

Referring to the drawing,l the.referenceV characters la and ib designate the track Ials of` a railway, and which rails are dividedinthe usual manner with a track section provdedrwithA a track circuit which includes the rails and a current source connected across the rails adjacent the exit end of the section. This track circuit current iscoded at any one of a plurality of different, code rates raccording to different traffic conditions. The trackway apparatus for supplying the coded current to rails la and ib is not shown since itV forms no partk of my invention and may be any one of several well-known arrangements. This trackway apparatus may be, for example, similar to that disclosed in Letters Patent Yof the United States No. 1,986,679, granted January 1,y 1935, to Lloyd V. Lewis, for Railway traffic controlling apparatus..

In order to better understand my invention, I shall assume that the current supplied to rails ld and lbI is an alternating current of the frequency of the order of 10U cycles per second,` and it is coded at the rates of 180,l 120 and 75 interruptions per minute to reflect clear, approachmedium 4and approach traiic conditions, respectively, the absence of rail current or the presence of non-coded current reiiecting slow speed traillc conditions. It is to be understood that the invention is not limited to the above mentioned frequencies and codes for the track circuit current,'and other frequencies and codes canbeused.

The train carried apparatus includes as essential elements, a receiver, an amplier unit, decoding means, acknowledging means, signaling means, and a J@est panel as well as a suitable source of power. Y

Thel receiver comprisesy inductors l and H which are mounted on the, train ahead of the leading pair of wheels, for inductive relationship with rails la and Ib, respectively. It follows that an electromotive force of a `frequency and code corresponding to that of the rail current is inductively picked up by each inductor 'lil and |.I. Thevalue of these electrornotive forces picked up from the track circuit will be proportional to the value ofthe track circuit current.

The two inductors I and Il, have their terminals. connected together at a junction box i2 to add their electromotive forces and the terminals of the junction box are in turn connected to input terminals FT andv TC of an amplifier unit to be described shortly, the connection including contacts 22, 23 land 24 of an acknowledging and cut-out switch ASW, as will be apparent from an inspection of the drawing.

The. acknowledging and cut-out switch, ASW is a three position manuallys operable switch having acknowledging position ACK, a normal position NOR and a cut-out position CO. This switchr ASW is provided with a handle,v not shown, `for moving it toitsr diierent positions and the switch would be mounted on the train where it is convenient to the train operator for operation by him. The arrangement of this switch is such that movable contact members I3 and l@ engage a stationary contact l5 at the acknowledging position ACK, movable contacts iiland H engage a stationary contact I8 at the normal position, movable Vcontacts i9 and 20 engage .a stationary Contact. 2l at the acknowledging position, and movable contacts 22 and 2 3; engage stationary contact 24 at both the normal `and acknowledging positions. At the cut-out position CO, all circuit connections are open.

Itis to be. pointed out that the train carried sourceof power for the cab signal apparatus may be any convenient direct current source, the terminals B32 and C of which are connected to a double pole cut-out switch PS. The voltage of this power source may be of any suitable value and preferably the cab signal apparatus is designed to use 32 volt direct current so that the usual train lighting source can be used to energize the cab signal apparatus without voltage conversion devices.`

The ampli-ner unit is indicated as a Whole by a dotted'rectangle AM. This amplier unit may take diierent forms, andvit may be similar to that disclosed in Letters Patent of the United States No. 2,336,766, granted December 14, 1943, to LeslieR. Allison, and Carl Volz, for Railway traiic controlling apparatus,- except to include an approved arrangement wherewith the value of voltage to be applied to-the input of the unit can be adjusted to take care of track circuits of highand low energy levels. This unit comprises as essential elements a lter Fl, an electron tube ET, a` master transformer MT, a code following relay MR and a decoding transformer DT.

The tube ET is disclosed as an indirectly heated tetrode which is designed for operation from a single 32 volt source of current, but other types of tubes can be used. A filament or heater 25 is connected across the B32v and C power leads through a resistor Ri for heating the tube. Two resistorsy R2 and R3 in series are connected across thepower source to provide a voltage divider from which suitable voltages are applied to the tube. anode-cathode circuit for the tube, extends from the positive `terminal oi the voltage divider, throughiwinding 2.6 of the master transformer MT, anode 21 and tube space to cathode 2BA and tothe junction terminal of resistors R2 andrRB oi the voltage divider, a by-pass capacitor C3 being preferably connected across winding 23 0i the master transformer. A screen grid or electrode 29 of the tube is connected directly to the positive terminal of the voltage divider.

The input ofthe tube E T is connected to the terminals TC and FT through a gain control unit BU, filter FI, and a tuning capacitor C'l. Specii'cally, a rst windingl) of Ya transformer TI of the lter is connected across terminals TC and FT through a selected portion of a variable resistor Rd, another resistor R5 and tuning capacitor Cl; and a secondL winding 3l of the transformer has one terminal connected to control electrode 32 of the tube through unit BU, and the other terminal `connected to cathode 28 of the tube through resistor R3 of the voltage divider. AnA adjustable capacitor C2 isv c'onnected across thewinding 3| of the transformer TI.l The gain control Unit BU' comprises a resistor and a capaciior' irl mlliple andai-motions in the usual manner for such devices and I have found that- With tube ET constructed vwith proper operating characteristics this unit may not be required and can be omitted from the input circuit of the tube.

It is clear that the input circuit for the tube can be tuned by the capacitor CI and filter Fl to pass only energy of the frequency of the track circuit current and to substantially suppress energy of other frequencies, and the magnitude of the voltage applied to the tube can be adjusted by selection of the connection to the different terminals of resistor R4.

The electrode or screen grid 29 of tube ET is provided with a positive potential with respect to cathode 28 equal to the voltage drop of resistor R2 and the control grid 32 is biased negative in potential with respect to the cathode by the voltage drop across resistor R3. This establishes a given normal anode circuit current, the anode current being preferably made substantially zero in the absence of input voltage. By this arrangement the direct current component of the anode circuit current caused by energy picked up from the track circuit is maintained approximately constant over a Wide range of the voltage of the train carried source because the voltage across resistor R3 varies directly with the voltage applied to the anode 21 and screen electrode 29. It also remains approximately constant over a Wide range of track circuit current because of the automatic gain control unit BU.

The master relay MR is preferably a stick polar relay operating to reversibly actuate its polar armature 34 in response to electromotive forces of opposite polarity and of a given value. The operating winding of relay MR is connected across secondary winding 33 of master transformer MT, and the relay is operated in step with the pulses of electromotive force induced in secondary winding 33 due to the on and off code periods of the electromotive force picked up by the receiver from the track circuit energy.

Two portions 35 and 36 of a winding Pl of decoding transformer DT are alternately supplied with direct current from the 32 volt source through the polar contacts 31 and 38 of the code following relay MR, a resistor R6 being preferably included in the circuit. Thus, an alternating voltage is created across winding PI of the decoding transformer when relay MR is operated, the frequency of the alternating voltage corresponding to the code rate at which relay MIR is operated. The winding PI of the decoding transformer is connected to the decoding means, which comprises three decoding units identied by the dotted rectangles DI80, DI2IJ and D15, and three decoding relays A, R and L, there being an individual decoding relay for each decoding unit. These three decoding units are similar except for their tuning and are preferably of the construction disclosed in my copending application for Letters Patent of the United States, Serial No. 660,961, led April 10, 1946, for Reactance devices, now Patent No. 2,446,624, granted August 10, 1948.

Looking at the decoding unit DI80, for example, it includes a transformer 39, a capacitor C5, and a rectier 40. The input terminals of the unit are connected across winding PI of the decoding transformer and the output terminals of the unit are connected to the respective decoding relay A. This unit D180 is tuned to resonance at the frequency of the alternating voltage created-in the ldecoding transformer when relay MR is operated at a rate corresponding to the 180 Similarly, the unit DIZ!) includes a transformerV 42, a capacitor C1 and a rectifier 4| and is con,- nected across winding PI of decoding transformer DT. It is tuned to resonance at the frequency of the alternating voltage created in the decoding transformer when relay MR is operated at the rate corresponding to the code rate of the track circuit current. Thus thev decoding relay R is effectively energized by current passed by the unit DI20 when relay MR is operated in response to track circuit current of 120 code rate but is ineffectively energized when relay MR is operated at other code rates. Y

Again, the unit D15 includes a transformer 43, a capacitor C8 and a rectifier 44 and is connected to Winding Pl of the decoding transformer. It is tuned to resonance at the frequency of the alter-` nating voltage created in the decoding trans,- former when relay MR is operated at the rate corresponding to the 75 code rate of the track circuit current, and thus the decoding relay L connected with the output terminals of the unit D15 is effectively energized in response to the '15 code of the track circuit current and is ineffectively energized in response to the other code rates.

It is to be pointed out that the decoding relay R is provided with an alternative energizing circuit Which includes power lead B32, front contact 45 of relay A, resistor 46, winding of relay R, front contact 41 of relay A, and power lead C. Thus when energy of the code rate is picked up from the track rails and decoding relay A is energized due to the operation of relay MR, the relay R is also energized due to its alternative circuit. Similarly, the decoding relay L is provided With an alternative circuit which includes power lead B32, back contact 48 of relay A, front contact 49 of relay R, resistor 50, winding of 17elay L, front contact 5| of relay R, back contact 52 of relay A, and power lead C. Consequently when energy of the 120 code rate is picked up from the track rails and the decoding relayR is energized due to the rectified current passed by the decoding unit D120, the relay L is also energized due to its alternative circuit.

The decoding relays govern operating circuits for a cab signal CS which is located in the cab convenient to the train operator. In practicing the invention, a plurality of cab signals similar to the signal CS are located on the train near the positions of different members of the train crew, but in the drawing only the one signal CS is shown for the sake of simplicity because the 1 other signals are duplications thereof.

The cab signal CS may take different forms and as shown it is a color light signal capable of displaying four distinctive aspects. When decoding relay A is picked up in response to track circuit energy of the 180 code, a signal operating circuit can be traced from power lead B32,`

through front contact 53 of relay A, Wire AA,v lamp 54 of signal CS, wire NA and front contact 41 of relay A to4 power lead C; and the lamp 54 is illuminated to display a green light as a clear sgnalindication. Whenrelay'A;isnreleascdand relay Rispickedup inresponse to track circuit:

cnergyof :the 120 code,l a. signal operating circuitv Y is-:formed from power lead B32 Ythrough back con-- decoding relays A and Ri released andlrelay: L Y

picked up-'in response to track circuit. energy of the-f1.5.V code, a signal operating. circuit` is formed from power lead B32 through back contacts 55 and 59 o'relays A vand R, respectively, front contact 60 of relay L, wire LL, lamp 6 I, wire NL, front contact t2v` of relay'L and back contacts 63 andV 52l=ofrelays lR and A, respectively, to power lead C; and lthe lamp 6i is illuminated to display a yellow light as an approach signalindication. Inthe-eventthe track circuit energy is shunted by a train in advance, the relay MR is not operated and all the decoding relays are released. Under this condition;Y a signal operating :circuit Vis formed from power lead B32 through back contacts 55,59; and' 6-4 of relays A, Rand L, respectively, wire, SS and lamp 65 to power lead'C, and the lamp 65 is illuminated to display a. red light Y as' a slow speed-indication.

. `Itjwas explained hereinbefore that relay R is energizedby its alternative circuit when the relay A is energized in response to the 189V code. Thus, a change from clear traic condition to approach-,medium traic condition changing the track circuit code from 180 to 120 lso that relay A. is deenergized .and relayR is energized through theassociated decoding unit,y there `is no .loss of. time in getting the decoding relayA R. picked up, to complete the approach-medium Signal 0perat-- ing circuit. Also, the possibility of a, redsignal flash duringthe change `in trafiic conditions yis minimized. Similarly,V when a change from approach-medium to approach traii'i'cconditions oc '611175. changing the track circuit code from 120" to 75`, there is no loss of time in getting therelay L picked up to` complete the approach cab signal circuit because relay. L is energized by` itsralternative circuit while the relay R is energizedby theV 120 code.

.An audible cab signalV in the form of an air. whistle is provided, thiswhistle being used to Warn the train operator of a change to a.,more, restrictive indication. This whistle, once. initiated, continues to sound until the.operator` acknowledges thecab .signalvchangc The whistleV 66is actuated through a magnet valve. the arrangement being such that when the., magnet Valveis energized thesupply o f air islol'ockedv and when deenergized the air supply is exhausted through theV whistle causing it `to sound. In

practicing my invention, several air whistles would Lpreferably be provided at dierent. points.

on the. train where. they would be heardby thediilerent members. of the train crew.

It is obvious that the. magnet valveMIifcan--be usedto. set into operation train brake controlling devices.. v

The magnet valve, MV s gQVerned througha group of acknowledging relays SP, LP .and RP and-the acknowledging switch ASW. It isbelieved, vthat the acknowledging .relays .and .their circuitsocan. best. beunderstood by .adescription of. theoperationof the. apparatus.

,In .describing thev operation of. the.aanparatus.

Issnau; met consider thotfoieor tramo conditionsexistyand; the track circuit current is'of the 180 code .so that the decoding relay A ispicked up inthe manner' explained hereinbefore. With re lay A picked up, the circuit for the clear cab signallighti 54* and the alternative circuit for the relay R. are closed. Also, a circuit is formed for the magnet valve this latter circuit extend'- ing from power lead B32, through front contact 45 of' relay A, wirel, back contact 68 of relay RP,l wirer M72, normally closed conta-ct 69 of a switch 96 ofV a test panel 'I'P- to be referred to later, wire MI, contacts I6,` t1 and I8 of switch ASW, wire M, winding of magnet valve MV, wire NM, back contact 'I0 of relay RPl and front contact Y'H of relay Ato power lead C'. It is to be noted'that a capacitor C4V is connected across theA current source in multiple with the winding of the magnet valveMV, and the capacitor C4 is normally charged at the voltage of the current source.

shall next assume that trac conditions change from clear to approach-medium changing theftrack circuit current from the tothe 120 code; This causes decoding relay A to be released, and decoding relay R to be energized by current passed by the associated decoding unit D-I20. Under these circumstances the approachmedium cab signal vt-I--S is illuminated and the decoding relay L is energized by its alternative circuit. The release of relay A opening front contacts 4'5 and 'Il opens the circuit for magnet valve MV and that valve is deenergized and the whistle 66 issounded to call attention to this change to thel more restrictive cab signal. 'Ihere is a delay period in the release of the magnet valve MV equal `to the discharge period of the capacitor C4 throughv the winding of the magnet valve. Capacitor C4 is selected to provide a predetermineddelay periodof the order of 2 seconds, although other delay periods can be used.

To silence the whistle, the train operator must move the switch ASWV to the acknowledging positionand then restore the switch toits normal position. .At the acknowledging position of the switch ASW current ows from power lead B32 through the contacts I3, I4 and I5 of switch ASW, wiregSPI, top winding of relay SP, resistor 12; wireNSP andcontacts I9, 20 and 2'I of the s witchi ASW to power lead C. This picks up acknowledging relay SP and with relay SP picked up the top winding of the relay LP is energized JoyA an obvious pick-up circuit including front contacts-Hand T4 ofrelay SP, and with relay LP picked up the; top winding of the acknowledging relaysRPis energized. by an obvious pickup circuit including front contacts 'l5 'and 'I6 of relay LP. Thatis to say, the. acknowledging-relays SP, LP andV RP are'picked. up in sequence. When switch ASW restoredto its normal position, the circuit forsrelay SPis opened and the relay is released. Therelease of relay SP opens the circuit :for the top'fwindifng of relay LP and relay LP is released, and` with relay LPfreleased the circuit for the topwi-nding ofrrelay RP isv open but relay RP is now provided with a holdingcircuit that extends from power lead B32, through back contact 48: of relay A, front contact 49` of relay R, frontA contact 'I-'I of relay RP, lower winding of therelay, resistor 18, front contact 'I9 of the re` lay, .front contact 800i relay Rand back contact 8.1 ,of` relay A to power lead. C. Thus, theaclmowledging.- relay RP remains energized `subsequent to .therestoringof theswitch ASW toits normal.

position and a circuit is formed for the magnet 9 Vvalve from power lead B32, through front contact 82 of relay RP, wire M2, contact 69, wire MI, contacts I6, l1 and I8 of switch ASW, wire 'M, winding of magnet valve MV, wire NM and front contact 83 of relay RP to power lead C. Magnet valve MV is now energized and the whistle 86 is made silent. Also the capacitor C4 is recharged.

I shall next assume that traiilc conditions change from approach-medium to approach, causing the track circuit current to change from the 120 to the '15 code. This causes relays R and A to be released and the relay L to be energized by current supplied through the associated decoding unit D15. With relays A and R released and relay L picked up, the approach cab signal 8l is illuminated. The previous traced holding circuit for the relay RP is opened at front contacts 4'9 and 88 of relay R and relay RP is released to open the circuit for the magnet valve MV and the whistle 66 is sounded. This time there is a delay period in the release of the magnet valve subsequent to the change of the position of the decoding relays which is equal to the release period of relay RP plus the discharge period of capacitor C4. Assuming the discharge period of capacitor C4 is of the order of 2 seconds and the release period of relay RP is of the order of one second, the delay in the sounding of the whistle subsequent to the change from approach-medium to approach is substantially three seconds or one second longer than the delay period when the code changed from clear to approach-medium.

To silence the whistle 66 the operator moves the switch ASW to the acknowledging position andr then back to the normal position the same as before. With the switch ASW at the position ACK the relays SP, LP and RP are energized in sequence as explained hereinbefore. When switch ASW is restored to its normal position the relay SP is released to open the pick-up circuit for relays LP but relay LP is now retained energized by a holding circuit, and which holding circuit receives power from power lead B32 through back contacts 48 and 84 of relays A and R, respectively, front contact 85 of relay L, front contact 85 of relay LP, lower winding of the relay, resistor 81, front contact 88 of relay LP, front contact 89 of relay L, and back contacts 90 and 8| of relays R and A, respectively, to power lead C. With relay LP picked up, then the relay RP is energized fby its pick-up circuit including its top winding, and with relay RP picked up it completes the traced for the magnet valve. Also, capacitor C4 is recharged.

I shall next consider that traffic conditions `change from approach to slow speed and the track circuit current is shunted or non-coded so that the relays A, R and L are all released. Under these circumstances the slowspeed cab signal '55 is iluminated. With relay L released, the relays LP and RP-v are deenergized one after the other and the magnet valve MV is without current and is deenergized to sound the whistle. This time the delay period between the release of the decoding relay L and the release of the magnet valve MV to sound the whistle is equal to the release period of relay LP, plus the release period of relay RP, plus the discharge period of capacitor C4. That is, the delay in sounding the whistle subsequent to the change from approach to the slow speed signal is made greater than the periodwhen traic conditions change circuit previously iii) l0 from approach-medium to approach. This arrangement tends to cause the whistle to blow at a more nearly xed distance beyond the code change point rather than after the expiration of a fixed time interval.

Algain, the operator must acknowledge this change to the slow speed signal by actuating the switch ASW to the acknowledging position and then back to the normal position in order to silence the whistle. With the switch ASW at the position ACK the relays SP, LP and RP are energized in sequence as before explained. A holding circuit for relay SP is now provided from the power lead B32 through back contacts 48, 84 and Si of the decoding relays A, R and L, respectively, iront contact 92 of relay SP, lower winding of the relay, resistor 83, front contact 9G of relay SP, and back contacts 95, 90 and 8| of the relays L, R and A, respectively, to power lead C. With relay SP retained energized then the other two acknowledging relays LP and RP are held energized by their pick-up circuits and with relay RP picked up the magnet valve is energized over the previously traced circuit and the whistle is made silent. Y

In the case the traffic condition-s change from slow speed to approach so that relay L is picked up the acknowledging relay SP is released but the two relays LP and RP remain energized and the energizing circuit for the magnet valve is not disturbed and the whistle is not sounded at this change to a less restrictive signal. Again, a change from approach to approach-medium condition wili result in relay R being picked up and thi-s causes the acknowledging relay LP to become deenergized but the relay RP is retained energized by its holding circuit and the circuit for the magnet valve is not disturbed so that the whistle does notblow for this change to a less restrictive condition. If trafc conditions change to clear so that the decoding relay A is energized, then the acknowledging relay RP is released but the magnet valve is now energized over its traced cir-cuit including front contacts and 1l of relay A, and the whistle is not sounded due to this change in trai-hc conditions.

I have found that by tuning the decoding unit D15 in place of having this unit responsive to al1 codes as heretofore provided, the changes ofa false indication due to intermittent circuit conditions is minimized. i y

Also the long retardation of the SP acknowledging relay as heretofore required in order to avoid loss of acknowledgment due to unnecessary picking up of decoding relay L is not required and relay SP can be made with a retardation of the same value provided for relays LP and RP. Furthermore, since the capacitor C4 provides the maior portion of the delay time between change of code downward and release of magnet valve MV, it is not necessary to provide so much retardation in thedecoding relays as has been the practice in the past. This permitsthe decoding relay to be made identical with the acknowledging relays with no larger copper ferrules for snubbing purposes than is necessary to insure that .the acknowledging relays .bridge the open circuit transition time of the decoding relays. The additional winding space thus obtained is utilized to increase the turns and the operating current for the decoding relay reduced, which reduction in operating current results in the aging of the rectifiers being reduced. These several features permit the decoding and acknowb edging relays to be made identical in construction and ccmplctely interchangeable, which vgreatly 'facilitates maintenance.VV In the case of .the acknowledging relays, the leads ci the usual two coilsare separated'and the two coils used'inde- Vpendently so that the pick-up and holding circuits of the acknowledging relays are insulated from each other. Y Y

The` apparatus including the amplifier unit, decoding means and acknowledging relays are housedlin an equipment box indicated by the dot j and ldash rectangle EB. This box is made weatherproof and it is mounted generally on the train at-some'point outside of the cab Vdue to the limited space in the cab. When the apparatus of the equipment boi; is remote from the position of the cab signal and acknowledging switch inthe cab, testing and inspection of the apparatus generally requires two workmenin order to properly check the different elements, that is,V

to check agreement between the dierent conditions of the apparatus in the equipment box and the VVcorresponding conditions of the cab -signal and acknowledging switch, To facilitate testing and: inspection, I provide a testpanel whichis made integral with the apparatus mounted in the equipment box. This test panel is indicated by a dotted rectangle TP and includes manually operable switches 96 and '91', test lamps 93 and 9S andY an'illurninating lamp i90. The lamp 9,9 is connected in multiple with slow speed lamp 55 of the cab signal when a contact I9! of the switch 9"! is closed and the test lamp 953 is connected in lll-2 of switch 9'5 is closed. Preferably the lamp 9e displays a'red light and theY light. The lamp i9@ is connected Yacross the Y power source through a conta-ct H13 of the switch 9'! `and lamp lili! serves to `illuminate the equipl ment box as an aid in testing the apparatus at night or when the` light i-s bad. Itr follows that when the switch 9'! isrclosed, the red lamp 99 indicates when all-the decoding relays are down `and the opallamp S8 when illuminated indicates when the magnet valve is energized.

The other switch 96' of the test `panel is a duplicate from a circuit standpoint of the acknowledging switch A'SW, the two normally open contacts G4 and 95 of switch SiS-being inlmultiple with contacts l5 and 2l, respectively, of the switch ASW. Also, contact 69 of switch 96 is in series with the contact I8 of switch ASW.

At terminals where testing and inspection of Ythe cab signal apparatus is generally done, a test track-circuit is provided and the locomotive is run onto this test track circuit. The maintainer can! check the normalrelease condition of the decoding relay by operating switch 9? and observing the lamp 9s. That is, the lamp Qilis illuminated whenever the test track circuit is deenergized and is dark'whenever a code is applied to the test track circuit. With any code of 'the vtest track circuit current, the acknowledging equipment can becheclredby operation of the'swi'tch 96 subsequent to a change in the .code of the'track circuitr current to a more restrictive code; Y It is'to be seen, therefore, that bythe provision YVof test panel TP at the equipment box, the apparatus can bev tested efciently and quickly bythe Y maintainer. alone and without the vmaintainer leaving the position of 'the equipment box and climbing into the locomotive cab.

kAlthough I have herein shown and describedbut Vone form of train carried cab signal apparatus embodying my invention, it is understood that various changes andimodications `may be lamp 98 an opal l2 made :therein within the scope 4of the Vappended claims without departing from the spirit and scope of my invention.

responding to the code rate Yof the track circuit current, a decoding transformer connected to said code following relay to create an alternating voltage of a frequency corresponding to the code rate at which therelay is operated; a first, a second and athird decoding unit connected in mul'- tipleto said transformer; each said decoding unit including capacitance and inductance to tune the first, second and third units to resonance at the frequency of said alternating voltages for the rst, second and third code rates, respectively; a rst, a second and a third decoding relay connected to said' first, second and third decoding unit, respectively', tio-effectively energize the first, second and third decoding relays in response to the rst, second and" third code rate, respectively; an alterna-'tive circuitincluding a current source and a Yfront contact of said first decoding relay Y connected to the second decodin-g relay to enermultiple with magnet valve MV when contact gize the second decoding relay, and another valternative circuit including a current source, a back contact of said first decoding relay and a, front contact of said seconddecoding relay connected-to saidV third decoding vrelay to energize the Y third decoding relay.

Gti

2.7In train'carried cab signal apparatus yfor use with track circuit current coded-at a first, a second and a third code rate` for operating a train carried code followingrelay at corresponding code rateaja decoding transformer connected to said code following relay to create an alternating voltage of a frequency vcorresponding to the code rate at Ywhich the relay is operated, three decoding units one for each of said code rates, three decoding relays one :for Veach of said decoding units, said decoding units having their inputs connected in multipleto said decoding transformer and their outputs Vconnectedto the respective decoding relays, each said decoding unit tuned to resonance at the frequency of the alternatingvoltage created when the code following relay is operated at the corresponding code rate to effectively energize each decodingV relay only in response to the respective code rate, a rst alternative circuit including a current source and a front contact 'of the decod'ing'relay responsive to said rst code rate connected to the decoding relay responsive to the second code rate;V and' a second alternative circuit Vincluding a current source, a back contact of the decoding relay responsive to therst code rate, and a front contact ofthe decoding relay responsive to the second code rate connectedto the decodingy relay responsive to said third fcoderate.

3. In train carried cabs'i'gnal apparatus for usefwith track circuit energy coded at a first, a second and Va third code rate for operating a train carried code following relay at a rst, second and third code ra/te, respectively; a first,

second and a third decoding relay controlled by a first winding of the third acknowledging relay to energize that relay, a second pick-up circuit including a front contact of said third acknowl edging relay and a rst winding of said second acknowledging relay to energize the second acknowledging relay, a third pick-up circuit including a front contact of said second acknowledging relay and a first winding of said first acknowledging relay to energize the rst acknowl edging relay; a rst holding circuit including a back contact of said first decoding relay, a front contact of said second decoding relay and a front contact and second winding of said first acknowledging relay; a second holding circuit including a back contact of each of said first and second decoding relays, a front contact oi said third decoding relay and a front contact and second winding of said second acknowledging relay; a third holding circuit including a back contact of each of said decoding relays and a front contact and second winding of said third acknowledging relay, a warning signal, an operating circuit including a front contact of said rst decoding relay to energize said signal, and an alternative operating circuit including a front contact of said rst acknowledging relay to energize said signal.

4. In train carried cab signal apparatus for use with track circuit energy coded at a rst, a second and a third code rate for operating a train carried code following relay at a iirst, a second and a third code rate, respectively; three decoding relays governed by said code following relay through tuned units to electively energize an individual one of the decoding relays in response to each of said code rates, three acknowledging relays, circuit means including a normally open manually controlled contact to energize said acknowledging relays in sequence in a denite o order, a rst holding circuit including a back contact of a iirst one of said decoding relays and a front contact of a second one of said decoding relays to retain energized a first one of said acknowledging relays, a second holding circuit including a back contact of each of said first and second decoding relays and a front contact of a third one of the decoding relays to retain energized a second one of said acknowledging relays, a third holding circuit including a back contact of each one of said decoding relays to retain energized a third one of said acknowledging relays, a signal controlling magnet valve, a capacitor; a rst control circuit including a source of direct current, a front contact of said first decoding relay and said magnet valve and capacitor in multiple to provide a given delay period in the deenergizing of the magnet valve when the code changes from the rst to the second code; and a second control circuit including said direct current source, a front contact of said rst acknowledging relay and said magnet valve and capacitor in multiple to provide a delay period equal to said given period plus the release period of said first acknowledging relay for deenergizing the magnet valve when the code changes from the second to the third code, and a delay period equal to said given period plus the release periods of said rst and second acknowledging relays in sequence when the code changes from the third code to no code.

LESLIE R. ALLISON.

REFERENCES CITED UNITED STATES PATENTS Name Date Allison et al. Apr. 9, 1947 Number 

